1. Field of the Invention
The present invention relates to a liquid crystal display used in a television receiver or a display section of an electronic apparatus.
2. Description of the Related Art
FIGS. 22A and 22B show an example of a configuration of an MVA (Multi-domain Vertical Alignment) type liquid crystal display. FIG. 22A schematically shows a sectional structure of a liquid crystal display panel 101. FIG. 22B shows a structure of one pixel of the MVA type liquid crystal display panel 101 as viewed in a direction normal to the display screen. As shown in FIGS. 22A and 22B, the liquid crystal display panel 101 has a TFT substrate 102 on which thin film transistors (TFTs) 110 are formed and an opposite substrate 103 on which a common electrode and a color filter (CF) layer are formed. The substrates 102 and 103 are combined using a peripheral sealing material 105. A liquid crystal layer 104 is sealed between the substrates 102 and 103. A predetermined gap (cell gap) is maintained by spacers 106 between the TFT substrate 102 and the opposite substrate 103. The call gap may be maintained at the predetermined value by spacers in the form of protrusions instead of the spacers 106. A polarizer 107 is disposed, for example, on a crossed Nicols basis on each of surfaces of the TFT substrate 102 and the opposite substrate 103 opposite to the sides of the substrate facing each other. A mounting terminal 108 for mounting a liquid crystal driving IC (not shown) is formed on the TFT substrate 102.
As shown in FIG. 22B, the TFT substrate 102 includes a gate bus line 112 formed to extend in the horizontal direction in the figure and a drain bus line 111 formed to extend in the vertical direction in the figure across the gate bus line 112 with an insulation film interposed between them. A TFT 110 for driving the pixel is formed in the vicinity of an intersection between the bus lines 111 and 112. A part of the gate bus line 112 serves as a gate electrode of the TFT 110. A drain electrode (D) of the TFT 110 is electrically connected to a drain bus line 111. A source electrode (S) of the TFT 110 is electrically connected to a pixel electrode 109 formed in a pixel region defined by the bus lines 111 and 112. A storage capacitor bus line 117 is formed so as to extend across the pixel region in parallel with the gate bus line 112. A storage capacitor electrode (intermediate electrode) 116 is formed at each pixel above storage capacitor bus line 117 with an insulation film interposed between them. A storage capacitor Cs is formed by the storage capacitor bus line 117, the storage capacitor electrode 116, and the insulation film sandwiched between them.
The pixel electrode 109 is formed with slits 114 which are blanks in the electrode material. Linear protrusions 115 are formed on the opposite substrate 103. The slits 114 and the linear protrusions 115 serve as alignment regulating structures for regulating the direction in which liquid crystal molecules (not shown) in the liquid crystal layer 104 are tilted when a voltage is applied. The pixel region is divided into domains in which liquid crystal molecules are tilted in four respective directions because of the slits 114 and the linear protrusions 115. Since the liquid crystal 103 is tilted in four directions, a bias of the viewing angle of the display panel is leveled when compared to that of a liquid crystal display in which a liquid crystal is tilted only in one direction. A significant improvement in viewing angle characteristics is thus achieved. Such a technique is referred to as a domain division technique.
FIG. 23 schematically shows a sectional structure of an MVA type liquid crystal display employing the domain division technique. FIG. 23A shows a state of the section observed when no voltage is applied to the liquid crystal layer 104. FIGS. 23B and 23C show a state observed when a voltage is applied to the liquid crystal layer 104. Referring to FIGS. 23A and 23B, the linear protrusions 115 serving as alignment regulating structures are formed on both of the opposite substrate 103 on which the pixel electrode 118 and a vertical alignment film 119 are formed in the order listed and the TFT substrate 102 on which the pixel electrode 109 is formed. Referring to FIG. 23C, the slits 114 serving as alignment regulating structures are formed only on the TFT substrate 102. Although not shown, the linear protrusions 115 may be provided on only one of the substrates.
As shown in FIG. 23A, liquid crystal molecules 120 are aligned substantially perpendicularly to a surface of the TFT substrate 102 when no voltage is applied. When a voltage is applied between the substrates 102 and 103, as shown in FIG. 23B, the liquid crystal molecules 120 are tilted in directions which are determined by the shape of the linear protrusions 115. As shown in FIG. 23C, when a voltage is applied between the substrates 102 and 103 in the structure formed with the slits 114, the tilting direction of the liquid crystal molecules 120 is determined by an effect of an electric field generated in the liquid crystal layer 104. Although not shown, some known liquid crystal display panels have a structure in which linear protrusions 115 are formed on either of substrates 102 and 103 and in which slits 114 are formed on the other substrate. Such a structure is most commonly used in existing MVA type liquid crystal displays.
Patent Document 1: JP-A-2-12
Patent Document 2: U.S. Pat. No. 4,840,460
Patent Document 3: Japanese Patent No. 3,076,938
Patent Document 4: JP-A-2002-333,870
FIG. 24 is a graph showing transmittance characteristics relative to applied voltages (T-V characteristics) of a VA (Vertically Aligned) type liquid crystal display. The abscissa axis represents voltages (V) applied to the liquid crystal layer, and the ordinate axis represents light transmittance. The curve A connecting black circles in the figure indicates T-V characteristics in a direction perpendicular to the display screen (hereinafter referred to as a square direction). The curve B connecting asterisks in the figure indicates T-V characteristics in a direction at an azimuth angle of 90° and a polar angle of 60° to the display screen (hereinafter referred to as an oblique direction). An azimuth angle is an angle measured counterclockwise with reference to the direction to the right of the display screen. A polar angle is an angle to a line vertical to the center of the display screen.
As shown in FIG. 24, there is a distortion of transmittance (luminance) in the vicinity of the region enclosed by the circle C. For example, transmittance in the oblique direction is higher than transmittance in the square direction for relatively low gradations appearing a voltage of about 2.5 V is applied, whereas the transmittance in the oblique direction is lower than the transmittance in the square direction for relatively high gradations appearing when a voltage of about 4.5 V is applied. As a result, there are small differences in luminance within the range of effective driving voltages when the screen is viewed in the oblique direction. This phenomenon is most significantly observes as variation of a color.
FIGS. 25A and 25B show variation of a view of an image displayed on a display screen. FIG. 25A shows the image as viewed in a direction square to the screen, and FIG. 25B shows the image as viewed in an oblique direction. As shown in FIGS. 25A and 25B, when the display screen is viewed in the oblique direction, the color of the image appears more whitish than the view in the square direction.
FIGS. 26A, 26B, and 26C show gradation histograms of three primary colors, i.e., red (R), green (G), and blue (B) in a reddish image. FIG. 26A shows a gradation histogram of red. FIG. 26B shows a gradation histogram of green. FIG. 26C shows a gradation histogram of blue. The abscissa axes of FIGS. 26A to 26C represent gradations (256 gradations at levels 0 to 255), and the ordinate axes represent rates of presence (%). As shown in FIGS. 26A to 26C, relatively high gradations of red and relatively low gradations of green and blue are present in this image at high rates of presence. When such an image is displayed on the display screen of a VA type liquid crystal display and viewed in an oblique direction, red which is a light tone turns relatively darker, and green and blue which are dark tones turn relatively lighter. Since differences in luminance between the three primary colors consequently become small, the color of the screen as a whole becomes whitish.
As thus described, an MVA type or VA type liquid crystal display is excellent in viewing angle characteristics in a direction square to the same. However, the liquid crystal display has a problem in that its viewing angle characteristics are not satisfactory because the display screen as a whole appears in a whitish color when it is viewed in a direction oblique to the same. The problem described similarly occurs on a liquid crystal display of the TN (Twisted Nematic) type that is a driving method according to the related art.